In Iraq there was no plan for the country other than to allow for foreign companies to invest "in the country". It created chaos. There had to be a liberal government. Problems created weren't solved but actively ignored.

In Syria, fighting both Syrian and ISIL forces isn't very useful. You either do everything to bring down the government and take responsibility for the consequences, supporting a strong, independent, viable government while giving financial support, or you fight ISIL (first). Technically, the US involvement is illegal now, but that's not a very good argument in itself. It does make it difficult for other countries to join the strikes.

Churchill and F D Roosevelt needed Stalin. Or we'd all speak Germanic (wait... we do speak Germanic. ).

It's never black or white. It's a nice, comforting illusion that there is white, but there isn't.